The disclosed invention is directed generally to head-up displays for vehicles, and more particularly is directed to a holographic head-up display which provides for increased reflectivity and image contrast.
Head-up displays are utilized in vehicles such as automobiles to produce virtual images of vehicle operating parameter indicators that appear to be ahead of the vehicle windshield and are therefore viewable by the vehicle operator without diversion of his or her eyes to an instrument panel inside the vehicle and without refocusing.
A known head-up display technique involves utilizing a reflection hologram supported by a vehicle windshield for producing a virtual image in the line of sight of the operator of the vehicle. The hologram can be a mirror hologram for providing the virtual image of an image source, or it can be an image hologram which produces a virtual image recreation of the recorded image in response to playback illumination. Due to various factors such as playback illumination angle and illumination source optical characteristics, the virtual images produced by holographic head-up displays might not have sufficient contrast or might not be sufficiently bright due to insufficient reflectivity of the hologram.